Data compositing and array control system

ABSTRACT

This abstract describes a system for acquisition of analog signals at a plurality of sensors, carrying these signals in groups of M channels to each of N spaced-apart array terminals, processing each signal in the array terminals by separately amplifying, digitizing to 1 bit and storing as single bit pulses, one for each channel, in a parallel to serial convertor. Each of the convertors in each of the array terminals are operatively connected in series and to an array controller, which also controls a disc magnetic recorder. On command, the convertors are read out in series as sequential trains of M bits into core memories and then stored on the disc. Successive, bit samples at subsequent digitizing intervals are stored on the disc, to form a first record. Subsequent records are processed, stored in core memory and composited with previous records stored on the disc.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 566,045, now U.S. Pat. No. 3,986,008, filed Apr. 7, 1975 entitled:Data Compositing and Array Control System, which is a continuation ofSer. No. 358,078, now U.S. Pat. No. 3,883,725, filed May 7, 1973.

This application is related to three other applications assigned to thesame assignee as this application and filed on the same date as thisapplication. The titles of the other three applications are as follows:Data Array Network System, Ser. No. 563,184 now U.S. Pat. No. 3,938,073continuation of Ser. No. 358,097, now U.S. Pat. No. 3,881,166; DataAcquisition and Storage system, Ser. No. 358,007; and Data Acquisitionand Processing System, Ser. No. 358,076 now U.S. Pat. No. 3,930,145.U.S. Pat. Nos. 3,883,725, 3,881,166 and Ser. Nos. 358,077 and 358,076now U.S. Pat. No. 3,930,145 are incorporated into this application byreference.

BACKGROUND OF THE INVENTION

This invention is in the field of data acquisition and processingsystems. More particularly, it is concerned with apparatus and methodsfor detecting analog signals at widely spaced locations, amplifyingthese signals and digitizing to 1 bit, and transmitting them as trainsof single bit digital pulses over a single pair of conductors to adistant recording point, and compositing pluralities of said signals.

Still more particularly, it concerns a system in which a plurality ofseparate detectors produce analog signals which are amplified, digitizedto 1 bit and transmitted by a two conductor cable to a disc recordingmeans, and there composited with succeeding repetitions of the signals.

While this invention is useful in the acquisition of any type of analogsignals such as in the field of data collection, vibration analysis,sonar signaling, nuclear technology, and so on, it is most appropriatelyuseful in the area of seismic prospecting and as a matter ofconvenience, and not in any limiting way, it will be discussed in thatapplication.

In the prior art systems the seismic signals detected by the geophoneshave normally been transmitted by separate pairs of conductors to therecording track. Here they are amplified in high gain, gain rangingamplifiers, multiplexed into sequential amplitude samples of successivetraces, and digitized to 15 or more bits, after which they aretemporarily recorded on a magnetic medium. The next repetition of theelastic wave signal is processed in a similar way and successiveamplitude measurements of given traces at a given time are summed, andthe sum is again recorded on the magnetic medium,

SUMMARY OF THE INVENTION

It is a primary objective of this invention to provide a dataacquisition, transmission and compositing system in which a greatplurality of separate geophone channels are coded and multiplexed andtransmitted to a recording means, and, under control of the recordingmeans, stored in preselected spaced locations, so that a second recordcan be transmitted to the recording means, added to the recordpreviously received, and the sum record rerecorded in the same storagelocations.

This and other objects are realized and the limitations of the prior artare overcome in the present invention which differs in a number of waysfrom the prior art systems. In particular, the plurality of seismicsignals that are detected in the field are divided into groups andprocessed in a plurality of array terminals, by being amplified,digitized to 1 bit and stored.

In each of the plurality of array terminals there are a differentplurality of geophone signals which are processed in a similar manner.The processed signals from all of the array terminals are impressed on acable which serially passes through each of the array terminals.

This cable is connected to an array controller in the recording unit ortruck. The array controller using a control pulse from the disc, sets upa timing procedure by which it initiates commands which are sent to thearray terminals to provide signal processing activities.

The geophone signal is sent to a comparator amplifier. There are aplurality of these, one for each of the M geophone channels in each ofthe N array terminals. These comparator amplifiers can be commandedsimultaneously to digitize the geophone signals to 1 bit. This producesa simultaneous plurality of short duration pulses which are either alogical 1 or 0, depending on whether the sign of the signal is plus orminus at the time of digitization of each channel. These 1 bit pulsesare passed in parallel to parallel to serial convertor where they arestored. This digitizing to 1 bit process is repeated at selectedintervals of time, the digitizing intervals, which may be one, two orfour milliseconds, etc. apart, for example. The parallel to serialconvertor is then commanded to read out the stored bits in serial order.These are read out and transmitted to the array controller on a twoconductor pair, which passes serially through each of the other arrayterminals. All of the array terminals sequentially read out the signalsstored in their convertors and send them through the next in seriesterminal, and so on to the storage in the array controller. Thus a firstsample from each trace of the entire plurality of NM traces is providedas a flow of 1 bit signals to the storage. These bits are first storedin core memory and then recorded on the disc, one in each appropriateaddress, which are arranged in an 8 bit spaced relation. The data aretransferred from each array terminal to the array controller and to thecore memories at the rate of the clock in that specific array terminal.They are then read out of core to the disc in accordance with the discclock.

This first sequence of bits represents all of the information on alltraces at the first digitizing interval. This procedure is repeated ateach digitizing interval on command from the controller, until thecomplete signal traces for the entire group of geophones has beenrecorded on the disc as a first record.

Next, a repetition of the elastic wave signal is impressed on the earth,and another complete set of channels are detected, amplified, digitizedto 1 bit and transmitted to core memory. There is not enough space inthe core memory to store a complete record. So when one bank of core isfilled, the composite of previously composited records are read out ofthe disc to core memory. Then samples of new data and previouslycomposited data are read out of core simultaneously, added, and thenstored back on the disc in the same spaced addresses.

When the full number of repetitions of sweeps to be run are completed,and all the traces are composited, the disc is filled. The disc is thenunloaded into core and then read out of core in single trace timesequential order, and sent to the processor. Thereafter, a second set ofsweeps are carried out and the geophone signals are brought in andrecorded on the disc, repeating the operation just described for thefirst set of sweeps.

Although the signals as transmitted from the array terminals to the discare 1 bit signals, by repetition of sweeps and compositing, the wordsrepresenting digitized measurements on each trace will accumulate up to8 bits, depending on the number of repetitions, such as 256. There isprovision for storage on the disc of up to 1,024 8 bit words, andsimilarly in the processor memory. The processor memory is now organizedon a trace storage basis so that complete traces can be read out insequence and sent to the Fast Fourier Transform box for processing byconvolution, or other processes.

The present invention is concerned with the disc, the core memories andthe array controller. These operate as a data compositor and arraycontroller. On very simple infrequent commands from the computer, thearray controller will provide appropriate detail commands, through aradio to the vibrator trucks, then through control wires in the arraynetwork cable, to control the signal processing in the array terminals,their digitization and storage, and sequential read out to the disc, andthe processing between the disc, the core memory banks and the adder inorder to do the compositing, and eventually the the read out of thecomposited data in trace form to the processor memory.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of this invention and a better understanding ofthe principles and details of the invention will be evident from thefollowing description taken in conjunction with the appended drawings inwhich:

FIG. 1 is a schematic diagram of the array terminals, array cablenetwork, the array controller, the core and disc storage systems and thecomputer. This is patterned after FIG. 1 of U.S. Pat. No. 3,883,725.

FIG. 2 is a schematic diagram of part of FIG. 1.

FIG. 3 is a schematic diagram of part of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings, and in particular, toFIG. 1. This shows in schematic form the entire system of the arraycontroller and associated apparatus, identified by the numeral 210. Thisis enclosed in the dashed line 213. The heart of the system is the arraycontroller 220 which controls magnetic disc 234 and the core memorybanks 238A, 238B, 239A and 239B.

The array terminal network indicated generally by the numeral 216 isfully described in a companion copending application Ser. No. 358,077;entitled Data Acquisition Transport and Storage System, which isincorporated into this application by reference.

The geophones are arranged in groups of M geophones, there being Ngroups of geophones connected to a corresponding N array terminal. Thegeophones identified by numeral 226A1, 226A2 . . . . 226AM are connectedin parallel to array terminal A, identified by numeral 226A. Similarly,geophones 226B1 to 226BM are connected in parallel to array terminal B,226B, and so on, until geophones 226N1 to 226NM are connected inparallel to array terminal N, 226N. The array terminals are connectedtogether by multiple conductor cables 228A, 228B, . . . .228(N-1).

The serially connected array terminals are connected by cables 230, tothe recording truck and to the array controller, 220. In the cable 230are a signal conductor pair and a plurality of control conductor pairs,which are controlled by commands from the array controller.

The procedure of operation is substantially as follows: On signal fromthe computer via bus 244 the array controller sets up a procedure whichis in accordance with the computer instruction, of address locations,and number of sweeps and similar information. The computer sends out asignal by lead 232 to the radio 222 and antenna 224, which sends a startsignal to the plurality of vibrators. The elastic wave signal from thevibrators passes through the earth and is detected by the plurality ofgeophones 226.

These geophone signals after amplification, are sent to a comparator.The comparator is commanded by the array controller at selectedintervals which occur at the digitizing interval, to sample and digitizeeach of the signals coming to the comparator. This is done by providinga high gain amplification and clipping, so that the output will be asquare wave signal having the same zero axis crossings as the originalsignal. These are connected through gates to the parallel inputs of aparallel to serial convertor. At each digitizing interval the gates aremomentarily opened and each storage element receives a logical 1 or 0dependent on whether the signal was plus or minus. These 1 or 0 bits arestored in the convertors in each of the array terminals. The details ofthese steps is fully described in the copending application: Ser. No.358,077 entitled Data Acquisition, Transport and Storage System.

At the times required for the digitizing intervals, these stored bitsare read out in sequence from each array terminal and impressed on thecables 228 through the next in series terminal and so on. Thus at eachdigitizing interval there are NM bits serially transmitted along thecable 230 and placed on the disc in preselected address locations.

As will be described in connection with FIG. 2, there are placed on thedisc, in spaced relationship, a pattern of bits at each digitizinginterval a total of NM single-bit words. This is repeated at eachdigitizing interval until a complete record is recorded. Next arepetition sweep signal is initiated by the vibrator trucks, in responseto the radio signal, and the same procedure of recording the geophonesignals is carried out, providing a second complete set of bitsrepresenting a second record of NM channels. While this second record isbeing recorded, the previously recorded first record is read off thedisc into core. These values, at the discrete digitizing intervals aresummed with the corresponding incoming signal values at each digitizingtime, to form a composite of the first and second records. These wordsare recorded back on the disc.

While each record is made up of 1 bit words, as the plurality of recordsare composited, the number of bits in each digitized value increases, upto a maximum of 8 bits for 256 repetitions.

These summed or composited records are stored on the disc in a crosstrace (or multiplexed) sequence, at each interval of time. After thedisc is loaded, the data are read off the disc in a different pattern ofreading, which demultiplexes the data, and converts it to trace sequencedata, and sends it to the computer memory for further processing. Eachof the 256 traces are then in timed sequence. They are 8 bit numbers andare ready for processing such as, for example, being passed to the FastFourier Transform box, where they can be filtered or any other similaroperation carried out.

While we speak of specific numbers of array terminals, channels,repeated sweeps and digitizing intervals, these are only by way ofexample, and this invention is adapted for use in any desiredconfiguration. As previously explained in the parent application, ofwhich this is a continuation-in-part, the compositing of successiverepetitive signals was done by controlling all of the data collectionand transmission operations in synchronism with the rotation of thedisc. There is a sensor which puts out a pulse at each unit rotation ofthe disc, corresponding to the position of an additional bit location oneach of the tracks. This was used to time the commands to call for dataout of the individual array terminals and to time the recording onto thedisc. Also as explained in Ser. No. 566,045, now U.S. Pat. No. 3,986,008digitized trace as it was recorded on the disc was retained in a specialset of addresses capable of storing single bits. These addressesretained that series of traces until the next series of tracescorresponding to the next record had been recorded, after which, the twosingle bit records were composited.

The purpose of retaining the current digitized record until thefollowing one was recorded, was to retain the ability to discard thatrecord in case it became evident that the data recorded on that recordwas of poor quality. In the course of operation of this equipment overthe extent of many hundreds of thousands of records, it became evidentthat this storage of a digitized record was not essential, and thereforea much simpler type of compositing was devised which is part of theinvention of this application and will be described in some detail.

In the parent application, Ser. No. 566,045, it was also designed tocarry the 1 bit digital signals from the array terminals directly to thearray controller and to the rotating disc. The disc then was the mastertime controller. Because of many variables which affected this type ofcontrol, a change has been made which will be illustrated in terms ofFIGS. 2 and 3. In this invention, while the disc initiates the commandsto the array terminals to transmit data, the data transmitted as trainsof single bit signals into the array controller are transferred at highbit speed into core memories, and are later transmitted at lower speedfrom the core memories into space allocations, on the various tracks ofthe disc. This desynchronizes the transmission of data from the arrayterminals to the array controller from actual storage of data on thedisc. Of course, the actual placement of data into the individualaddresses on the tracks from core memory is still timed by the discclock as the disc rotates.

This arrangement of data collection and storage is illustrated in a veryschematic manner in FIG. 1 by showing the data from array terminals onlead 230 passing into the array controller, and a disc 234 attached byleads 242 to the array controller, and a core memory bank comprisingfour separately addressable memories 238A, 239A, and 239B, 238B. Theseare grouped in two sets of two, that is, a 238 bank and a 239 bank. Oneset of these is reserved for incoming data which are transferred by thearray controller from the incoming data lead 230 into one bank whilepreviously recorded data from the disc are recalled from the disc andstored in the second bank. Corresponding data, at an individualdigitizing time can be simultaneously drawn out of one bank, and theother bank, composited and then re-stored on the disc.

Referring now to FIG. 2 there is shown in schematic form, but in greaterdetail, the manner in which the data are composited. There are two banksof memories indicated generally by the numerals 10 and 12. One of these10, comprises memories 14, 15. These are reserved for storage ofincoming new data which come in along the line 20 and are alternatelyloaded into 1A and 1B in accordance with the arrows 22 and 24. These areswitched by switch 20A to either 22A or 24A. There are two output leadsfrom the core memories 1A and 2A which go by leads 32, 34 and 36 to anadder 28. Line 36 is connected through switch 36A to either 32A or 34A.

There are two other banks of core memories 2B, and 2A. These arereserved for the storage of previously recorded data, which are read outof the disc, 26 by leads 44 and are loaded alternately by leads 46 and48 into the two memories 16 and 17. Line 44 connects through switch 44Ato either 46A or 48A.

There are output leads 38, 42 and 40 which from the two banks 16 and 17by either lead 38 or 42, and lead 40 to the adder 28. Lead 40 isswitched by 40A to either 38A or 42A. The switching of the switches 20Aand 36A is provided to "ping-pong" the memories. Thus while 20A isloading into 1A, 1B is unloading through 34 and 36A. Similarly, while 2Ais loading through 44A, to 17, 2B is unloading through 38 and 40A.

Incoming data along line 20 will go first through 20A and arrow 22 intobank 14. When this becomes filled, the incoming stream of data are thenswitched by the computer to line 24 for example, into the second bank15. While the second bank 15 is being loaded the data in bank 14 areread out to the adder 28, line 50 and through a small buffer 30, andthrough lead 52 onto the disc 26. This is the path for the first record.On the second record while data are coming in through line 22 into bank14, data previously composited on the disc 26 are read out through leads44, 44A and 46 into bank 17. While this is being done previously loadeddata from the disc into bank 16 and previously loaded new data in bank15 are drawn out through leads 40 and 36 respectively into the adder 28where they are added or composited, transmitted through leads 50 to theone word buffer 30 and through leads 52 to the disc 26.

The purpose of the one word buffer is to precisely time the flow of thecomposited data onto the disc. Since the data can be read out of thebuffer with for more precision than the disc can be positioned. The discclock is the source of clock signal to unload the buffer 30 onto thedisc, and therefore a small one word buffer 30 is utilized. The adder isof conventional design and needs no further explanation.

Each of the banks 14, 15, 16 and 17 are comprised of 4,096 16 bit words.Each of the 16 bit words is composed of one bit each from 16 geophonecircuits which are transmitted from each of the array terminals. Thissystem of single bit digitized signals can provide great speed oftransmission from a great many individual channels, without havingextraordinary large memories and without being slowed down by theinput-output speed of the equipment such as the disc. However, becausethe speed of transmission of data from array terminals to the arraycontroller can be done so much more rapidly than actual loading andunloading data from the disc the use of the core memory banks 14, 15, 16and 17 provides a greater efficiency of operation.

Referring now to FIG. 3 there is shown in somewhat more detail, althoughstill in schematic form, the apparatus for compositing.

As shown in FIG. 1 the computer 212 contains a central processing unitC.P.U. 223 and has a working core memory 221. A bus 244 connects thecomputer to the array controller. In FIG. 3 this is illustrated by thearrow 74 which indicates a line of communication between the centralprocessing unit 223 and the compositor 66. As in all computerinstallations, there must be an interface between the C.P.U. and theapparatus, such as the disc, and this is called an Input/Output (I/O)interface 60.

Data going to the disc arrives by way of the array terminals 64A and 64Band additional terminals indicated by the arrows 77N and 78N. Commandshave one line of transmission out, and in, from and to, the arraycontroller 62. Data are transmitted inward from the most remote arrayterminal through terminals 64B and 64A, by means of arrows 78N and 78Aand channel 78, into the array controller.

Commands to the array controller go from the C.P.U. through theinterface 60, and line 75. These commands can be processed by the arraycontroller and pass out along the series of array terminals and lines77. In response thereto data come in in according with the arrow 78 intothe array controller. The data then go from the array controller 62,which controls the compositor 66 which controls the flow of data byarrow 63 and bus 61 to and from the 4 memory banks 14, 15, 16 and 18.The compositor is also connected by lines 65 to a magnetic disc 70. Thusthe data are recorded on the disc by going from the array terminals,through line 78 to the array controller, through line 76 to thecompositor 66, and through lines 63 and 61 to the memory. They are thendrawn out of the memory by means of line 61 and 63, to the compositor66, and then out through 65 to the disc 70.

When new data come in through the previously described route and areloaded into the memory bank, old data are read off of the disc and go byway of line 65 to compositor 66 and lines 63 and 61 to the memory bank.Then, as previously described when the banks are filled, the incomingnew data, and incoming processed or stacked or composited old data, areswitched to the other of each pair of banks. Then data are read out ofthe two banks, one containing words of previously composited data, andthe other, words of the new data. They flow into the compositor, wherethey are added and then are buffered onto the disc 70 as shown in FIG.2.

The detail of the array terminals and the geophones, and the manner ofdigitizing to 1 bit the geophone signals in the array terminals, storingthem and then transmitting them serially through the array terminals tothe array controller, are described in greater detail in a companionapplication, Ser. No. 358,077.

The array controller 62 is in a sense a small specialized computer whichis controlled by the C.P.U. 223, and which handles operations, of whichthere are a great many repetitions. The programs for these are wiredinto the array controller, and therefore can be carried out at greatspeed and efficiency. Since the part of programming such controllers hasbeen described in the parent application and is well-known in the art nofurther details of the controller 62 is necessary. A similar statementcan be made for the I/O interface 60.

The storage of data on the 256 tracks on the disc 70 is a matter ofprogramming, and since the programming of discs for the transmission ofdata from memory to disc, and vice versa, through the control of aC.P.U. is well-known in the art, no further information need besupplied.

The data that are transmitted into the array controller are brought inin time multiplexed form. That is, each separate sequential bitcomprises one sample from one trace at one instant of time. Anothertrain of single bit values are transmitted at the next digitizing time,and so on. It becomes important then in the programming to provide meansfor arranging the data in the core memory and on the disc so that themultiplex form of data coming in to the system, can be put on to thedisc in multiplexed form. Later when all records are composited, theyare to be read out through the computer to a processing apparatus insuch a way that the output stream of data will give, in sequentialwords, the time sequential words of a single trace. Thus after the datahave been composited on the disc they can be read out and back to thememory, and then read out from the memory through the compositor andthrough output lead 72 through the I/O interface 60 and to the C.P.U.223, and to other apparatus, such as the Fast Fourier Transformprocessor, and so on.

As previously explained, the data in the core memory banks are made upof 16 bit words, which fit the size of each bank of single bit signalscoming in through the array terminal. Furthermore, as the one bitsignals are composited, depending on the number of traces composited,the number of bits for the words may go up to a maximum of 8 bits.Consequently, in the memory, which stores the composited data, these two8 bit words are stored in each of the 16 bit memory locations. Thus, twowords are simultaneously withdrawn from the A bank and the B bank, ateach operation of compositing so that four words are withdrawn andsummed and then returned to the disc, as two sum words.

In the design of this equipment and its layout in the field, there canbe any number of array terminals and correspondingly any number ofgeophones per array terminal. However, the capability in terms of totalnumber of channels of geophones is tied up with the size of the corememories and the disc, and so on. Consequently, there is a practicallimit to the number of individual channels that can be handled on asingle cable, in series, through a plurality of array terminals. Forconvenience, this present equipment utilizes 16 array terminals inseries, each with 16 separate channels of geophones, for a total of 256separate channels. Now, let us say the storage capability on the disc,and the processing capability, is provided for a total of 1,024channels. It is possible therefore to have four sets of cables each with256 channels. Or it is possible to have one single cable, comprising 64terminals with 16 channels each, for example, or four cables each with16 array terminals each with 16 channels. So any combination of 1,024total channels can be provided.

While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of construction and the arrangement of components. It isunderstood that the invention is not to be limited to the specificembodiments set forth herein by way of exemplifying the invention, butthe invention is to be limited only by the scope of the attached claimor claims, including the full range of equivalency to which each elementor step thereof is entitled.

What is claimed:
 1. In a data recording system having a repetitivesource, in which on each repetition of said source one or more analogsignals are detected, amplified and digitized to 1 bit, which arestored, and said stored 1 bit signals are read out of storage atselected command intervals to form trains of single bit signals, andsaid trains are transmitted to a data recording means, the method ofrecording and compositing said trains of single bit signals comprisingthe steps of:(a) running a rotating magnetic digital recording means ata substantially constant speed, said recording means having a pluralityof spaced multi-bit storage locations; (b) responsive to a first commandproducing said first train of single bit signals representative of afirst source; (c) recording in sequence, in a first digital memory eachof the bits in said first train; (d) transferring said first train ofsingle bit signals to said rotating magnetic digital storage means insaid spaced multi-bit address locations; (e) repeating said source for asecond time and responsive to a first command producing and transmittingto and recording in said first digital memory a second train of singlebit digital signals representative of a second source; (f) reading outfrom said rotating magnetic digital recording means said digital signalsstored in said spaced locations and transferring them to a seconddigital memory; (g) simultaneously reading samples of said second trainof single bit signals from said first memory and said digital signalsfrom said second memory; (h) adding said two signals to form a sumsignal; and (i) storing said sum signals back on said rotating storagemeans in said spaced multi-bit locations.
 2. The method as in claim 1 inwhich said system is a seismic geophysical system and in which saidanalog signals are geophone signals.
 3. The method as in claim 1 inwhich said magnetic digital recording means comprises disc means.
 4. Asignal detecting, coding and multiplexing system comprising:(a) aplurality of detectors generating analog signals representative ofphysical parameters, and means to amplify said analog signals atconstant gain; (b) digital storage means having a plurality ofsequential multi-bit address locations; (c) means to generate firstcommands at first time intervals and means responsive to said firstcommands to convert said analog signals to single bit digital signals,and means to store said digital signals; (d) means to read out saidstored digital signals in the form of a first train of sequential singlebit signals and to transmit said signals to a recording unit; (e) meansin said recording unit to store said first train of sequential singlebit signals in a first digital memory; (f) means to transfer said singlebit signals from said first digital memory to said digital storagemeans; (g) means to produce and transmit to and store in said firstdigital memory a second train of sequential single bit signals,responsive to a second plurality of analog signals; (h) means towithdraw from said digital storage means said digital signals stored insaid sequential address locations, and to store them in a second digitalmemory; (i) means to withdraw from said first and second digitalmemories corresponding, contemporaneous samples of said second train andsaid digital signals; (j) means to add said samples of said second trainand said digital signals to form sum signals; and (k) means to recordsaid sum signals on said digital storage means in said sequentialaddress locations.
 5. The method of detecting, digitizing to 1 bit,multiplexing and stacking a plurality of sequential analog signals froma repetitive source, comprising the steps of;(a) operating said sourcefor a first time' (b) generating analog signals representative ofphysical parameters of the earth responsive to said first operation ofsaid source, and amplifying said signals at constant gain; (c)converting said analog signals to 1 bit digital signals and storing said1 bit digital signals; (d) reading out said stored 1 bit digital signalsin the form of a first train of sequential 1 bit signals andtransmitting said train of 1 bit digital signals to and storing them ina first digital memory; (e) transferring said first train of sequential1 bit digital signals from said first digital memory to a digitalstorage means having a plurality of sequential multi-bit addresslocations; (f) producing, transmitting to, and storing in said firstdigital memory a second train of sequential single bit digital signals,responsive to a second plurality of analog signals, responsive to asecond repetition of said source; (g) withdrawing from said digitalstorage means said digital signals stored in said sequential multi-bitaddress locations, and storing them in a second digital memory; (h)withdrawing from said first and second digital memories correspondingsamples of said second train and said digital signals; (i) adding saidcorresponding samples of said second train and said digital signals toform sum signals; and (j) storing said sum signals in said digitalstorage means in said sequential multi-bit address locations.
 6. Themethod as in claim 5 in which said digital storage means havingsequential multi-bit address locations comprises rotating magneticdigital recording means.
 7. The method as in claim 5 in which said firstdigital memory comprises two separate half memories, whereby when saidfirst train of 1 bit digital signals is being transfered from a firsthalf memory to said digital storage means, said second train of 1 bitdigital signals is being stored in the second half memory of said firstdigital memory.